Frame and training pattern structure for multi-carrier systems

ABSTRACT

A transmitting apparatus for transmitting signals in a multi carrier system on the basis of a frame structure, each frame comprising at least two preamble patterns adjacent to each other in the frequency direction and at least two data patterns, said transmitting apparatus comprising a pilot mapper configured to map the same sequence of pilot signals on frequency carriers of each of said at least two preamble patterns in a frame, each preamble pattern having the same length, a data mapper configured to map data on frequency carriers of said at least two data patterns in a frame a transformer configured to transform said preamble patterns and said data patterns from the frequency domain into the time domain in order to generate a time domain transmission signal, and a transmitter configured transmit said transmission signal.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation application of U.S.application Ser. No. 12/437,161, filed May 7, 2009, the entire contentsof which are incorporated herein by reference. This application alsoclaims priority to European Patent Applications Nos. 08157549.0, filedJun. 4, 2008; 08157548.2, filed Jun. 4, 2008; 08158271.0, filed Jun. 13,2008; and 08158274.4, filed Jun. 13, 2008.

The present invention is directed to a new frame and training patternstructure for multi-carrier systems.

The present invention is hereby mainly directed (but not limited) tobroadcast systems, such as for example cable based or terrestrialdigital broadcast systems, in which content data, signalling data, pilotsignals and so forth are mapped on to a plurality of frequency carriers,which are then transmitted in a given overall or complete transmissionbandwidth. The receiver typically tunes to a partial channel (part ofthe overall transmission bandwidth) out of the complete transmissionbandwidth (sometimes called segmented reception) in order to receiveonly the content data which are necessary or wanted by the respectivereceiver. For example, in the ISDB-T standard, the overall channelbandwidth is hereby divided into 13 fixed segments of an equal length(equal number of frequency carriers).

The object of the present invention is therefore to provide atransmission apparatus and method as well as a signal structure for amulti-carrier system, which allows a receiver to be flexibly tuned toany required part of the overall transmission bandwidth.

The above object is achieved by a transmitting apparatus. Thetransmitting apparatus according to the present invention is adapted totransmit signals in a multi-carrier system on the basis of a framestructure, each frame comprising at least two training patterns adjacentto each other in the frequency direction and at least two data patterns,whereby the transmitting apparatus comprises pilot mapping means adaptedto map the same sequence of pilot signals on frequency carriers of eachof said at least two training patterns in a frame, each training patternhaving the same length, data mapping means adapted to map data onfrequency carriers of said at least two data patterns in a frame,transforming means adapted to transform said training patterns and saiddata patterns from the frequency domain into the time domain in order togenerate a time domain transmission signal, and transmitting meansadapted to transmit said time domain transmission signal.

The above object is further achieved by a transmitting method. Thetransmitting method according to the present invention is adapted totransmit signals in a multi-carrier system on the basis of a framestructure, each frame comprising at least two training patterns adjacentto each other in the frequency direction and at least two data patterns,whereby the method comprises the steps of mapping the same sequence ofpilot signals on frequency carriers of each of said at least twotraining patterns in a frame, each training pattern having the samelength, mapping data on frequency carriers of said at least two datapatterns in a frame, transforming said data patterns into the timedomain in order to generate a time domain transmission signal andtransmit said time domain transmission signal.

The above object is further achieved by a frame pattern. The framepattern of the present invention is adapted for a multi-carrier systemand comprises at least two training patterns adjacent to each other inthe frequency direction and at least two data patterns, wherein the samesequence of pilot signals is mapped on frequency carriers of each ofsaid at least two training patterns in the frame, each training patternhaving the same length, and wherein data are mapped on frequencycarriers of said at least two data patterns in the frame.

The object of the present invention is further to provide a receivingapparatus and method, as well as a system and a method for transmittingand receiving signals in a multi-carrier system, which allow a flexibletuning to any required part of the transmission bandwidth.

The above object is achieved by a receiving apparatus. The receivingapparatus according to the present invention is adapted to receivesignals in a multi-carrier system on the basis of a frame structure in atransmission bandwidth, each frame comprising at least two trainingpatterns adjacent to each other in the frequency direction each with thesame sequence of pilot signals mapped on frequency carriers and at leasttwo data patterns with data mapped on frequency carriers, each of saidat least two training patterns having the same length, wherein saidreceiving apparatus comprises receiving means adapted to be tuned to andto receive a selected part of said transmission bandwidth, said selectedpart of said transmission bandwidth having at least the length of saidtraining patterns and covering at least one data pattern to be received,and correlation means adapted to perform a correlation on the basis ofthe pilot signals received in said selected part of said transmissionbandwidth.

The above object is further achieved by a receiving method. Thereceiving method of the present invention is adapted to receive signalstransmitted in a multi-carrier system on the basis of a frame structurein a transmission bandwidth, each frame comprising at least two trainingpatterns adjacent to each other in the frequency direction each with thesame sequence of pilot signals mapped on frequency carriers and at leasttwo data patterns with data mapped on frequency carriers, each of saidat least two training patterns having the same length, whereby themethod comprises the steps of receiving a selected part of saidtransmission bandwidth, said selected part of said transmissionbandwidth having at least the length of one of said training patternsincorporating at least one data pattern to be received, and performing acorrelation on the basis of the pilot signals received in said selectedpart of said transmission bandwidth.

The above object is further achieved by a system for transmitting andreceiving signals, comprising a transmitting apparatus for transmittingsignals in a multi carrier system on the basis of a frame structure,each frame comprising at least two training patterns adjacent to eachother in the frequency direction and at least two data patterns, saidtransmitting apparatus comprising

pilot mapping means adapted to map the same sequence of pilot signals onfrequency carriers of each of said at least two training patterns in aframe, each training pattern having the same length,

data mapping means adapted to map data on frequency carriers of said atleast two data patterns in a frame,

transforming means adapted to transform said training patterns and saiddata patterns from the frequency domain into the time domain in order togenerate a time domain transmission signal, and

transmitting means adapted to transmit said time domain transmissionsignal, said system further comprising a receiving apparatus accordingto the present invention adapted to receive said time domaintransmission signal from said transmitting apparatus.

The above object is further achieved by a method for transmitting andreceiving signals, comprising a transmitting method for transmittingsignals in a multi carrier system on the basis of a frame structure,each frame comprising at least two training patterns adjacent to eachother in the frequency direction and at least two data patterns, saidtransmitting method comprising the steps of

mapping the same sequence of pilot signals on frequency carriers of eachof said at least two training patterns in a frame, each training patternhaving the same length, mapping data on frequency carriers of said atleast two data patterns in a frame, transforming said training patternsand said data patterns from the frequency domain into the time domain inorder to generate a time domain transmission signal, and transmittingsaid time domain transmission signal,said method further comprising a receiving method according to thepresent invention adapted to receive said time domain transmissionsignal.

The present invention therefore suggests a multi-carrier system whichuses a frame structure or frame pattern in the frequency domain as wellas in the time domain. In the frequency domain, each frame comprises atleast two identical training patterns (which could also be calledpreamble patterns), which respectively carry the identical pilot signalson frequency carriers and respectively have the same length (orbandwidth). After a conversion into the time domain, in the resultingtime domain signal, each frame then comprises a respective preamble (ortraining) symbol as well as data symbols. Each frame pattern covers theentire or overall transmission bandwidth in the frequency direction, sothat the overall transmission bandwidth is therefore equally divided bythe respectively identical training patterns. The data patterns of eachframe then follow the training patterns in time. The receiving apparatuscan be freely and flexibly tuned to any wanted part of the transmissionbandwidth, provided that the part of the transmission bandwidth to whichthe receiving apparatus can be tuned has at least the length of one ofthe training patterns. Hereby, the receiving apparatus is always able toreceive the pilot signals of an entire training pattern, so that acorrelation of the received pilot signals in order to provide a timesynchronisation, i.e. in order to define a synchronisation point or thestart of a next frame, and/or a frequency offset calculation and/or achannel estimation is/are possible in the receiving apparatus.

Advantageously, the length of at least some of the data patterns isdifferent from each other and the length of each of the data patterns issmaller than or equal to the length of each of the training patterns.Alternatively, the length of all the data patterns is the same andsmaller than or equal to the length of each of the training patterns.Hereby, the receiving apparatus can be tuned to any wanted part of thetransmission bandwidth in a flexible and non limited manner, whereby acorrelation and thus a time synchronisation is always possible since thepilot signals of an entire training pattern can be received, so that thereceiving apparatus can receive any wanted data pattern.

Further advantageously, the length of the data patterns in thetransmitting apparatus is adjusted dynamically. The multi-carrier systemwith the frame structure as suggested by the present invention thusenables a very flexible transmission of data content in which the lengthof data patterns, and thus the amount of data per data pattern can bedynamically changed, for example from frame to frame or in any otherrequired way. Alternatively, the length of the data patterns may befixed or permanent.

Further advantageously, the at least two data patterns succeed said atleast two training patterns in the time dimension, wherein each framecomprises additional data patterns succeeding said at least two datapatterns in the time dimension, each of said additional data patternshaving the respective same length as the corresponding one of saidprevious at least two data patterns. In other words, the structure ofthe data patterns in each frame is advantageously set up in a way thatat least two data patterns are arranged next to each other in thefrequency dimension so that the entire transmission bandwidth iscovered. Additional data patterns are then arranged in the same framebut following the at least two data patterns in the time direction,whereby each additional or following data pattern has the same length(in the frequency dimension or direction) as the previous data pattern.Thus, if a receiving apparatus is tuned to a specific part of thetransmission bandwidth, at least two data patterns per frame arereceived, each of said data patterns having the same length butfollowing each other in the time dimension.

Further advantageously, each frame comprises at least two signallingpatterns, whereby signalling data are mapped on frequency carriers ofeach signalling pattern in a frame. Each signalling pattern may herebyhave the same length in the frequency dimension. For example, everysignalling pattern in a frame may hereby have the identical signallingdata mapped onto its frequency carriers. Alternatively, the signallingdata of each signalling pattern in a frame may comprise the location ofthe signalling pattern in the frame, in which case every signallingpattern in a frame has the identical signalling data mapped onto itsfrequency carriers except the location information, which is differentat least for some each signalling patterns in each frame. Thus, eventhough a receiving apparatus only receives a part of the entiretransmission bandwidth, it is still possible to receive the entiresignalling data. Hereby, it is further advantageous if the length ofeach signalling pattern is the same as the length of the trainingpatterns and if the signalling patterns are aligned to the trainingpatterns in the frequency direction. In specific applications, it may,however, be advantageous if the length of each signalling pattern issmaller than the length of each of said training patterns. Hereby, itmay be particularly advantageous if the length of each signallingpattern is half the length of each of said training patterns.

Further advantageously, the signalling data are mapped on frequencycarriers of each signalling pattern with an error detection and/orcorrection coding. Hereby, even if a receiving apparatus cannot receivean entire signalling pattern, the receiving apparatus may still be ableto obtain the entire signalling information contained in the signallingpattern.

Advantageously, an auto-correlation is performed on the basis of thepilot signals received in the selected part of the transmissionbandwidth. Although the receiver can be flexibly tuned to any wantedpart of the transmission bandwidth, it is always possible to receive thepilot signals of an entire training pattern due to the new framestructure suggested by the present invention. Even if the selected partof the transmission bandwidth to which the receiver is tuned does notcompletely and correctly match with one of the training patterns (in thefrequency direction), the receiver will in such cases receive the lastpart of a (frequency wise) preceding training pattern and the first partof a (frequency wise) succeeding training pattern. Since each of thetraining patterns is identical, the receiver is able to perform anauto-correlation in order to obtain the wanted time synchronisationwithout any problems even without any reordering or other processing ofthe received pilot signals. Alternatively, in case that the receivingapparatus knows its (frequency dimension) offset from the trainingpattern structure in each frame, it may be able to re-arrange thereceived pilot signals in the original sequence of pilot signals, inwhich case a cross-correlation can be performed by comparing a storedversion of the training pattern with the received (re-arranged) versionof the training pattern received in the selected part of thetransmission bandwidth. In some applications, a cross-correlation mayresult in an even more accurate determination of the timesynchronisation as compared to an auto-correlation.

Further advantageously, in case that each frame comprises at least twosignalling patterns (in addition to the training and the data patterns),whereby each signalling pattern comprises signalling data mapped ontofrequency carriers, the receiver of the present invention is adapted toreconstruct the original signalling pattern from the received selectedpart of the transmission bandwidth. Each signalling pattern may herebyhave the same length in the frequency dimension. For example, everysignalling pattern in a frame may hereby have the identical signallingdata mapped onto its frequency carriers. Alternatively, the signallingdata of each signalling pattern in a frame may comprise the location ofthe signalling pattern in the frame, in which case every signallingpattern in a frame has the identical signalling data mapped onto itsfrequency carriers except the location information, which is differentat least for some each signalling patterns in each frame. For example,in case that the part of the transmission bandwidth to which thereceiver is tuned does not match with the signalling pattern structure(in the frequency dimension), the receiver might know its offset fromthe original signalling pattern and would therefore be able to rearrangethe received signalling signals and to bring them into the originalsequence or order so that all necessary signalling data can be correctlyidentified and further used. Alternatively, the receiver may comprisethe possibility to perform an error detection and/or correction decodingon the received signalling signals in order to reconstruct the originalsignalling pattern. Hereby, the transmitted signalling patterns maycomprise additional error coding, redundancies or the like enabling thereceiver to reconstruct the original signalling pattern even if only apart of the signalling pattern can be received.

Advantageously, the receiver is adapted to be tuned to and to receive aselected part of said transmission bandwidth so that an optimizedreceipt of a signalling pattern in the selected part of the transmissionbandwidth is enabled. Particularly if the frequency dimension structureof the data patterns and the signalling patterns in a frame do notmatch, and if the selective part of the transmission bandwidth to bereceived in the receiver is larger (in frequency dimension) than thedata pattern(s) to be received, it may be possible to optimize thetuning so that the best possible receipt of a signalling pattern isachieved, for example by adjusting the tuning so that the maximum partof one entire signalling pattern is received while still receiving theentire wanted data pattern(s).

Generally, it may be advantageous to tune the receiver so that theselective part of the transmission bandwidth is received so that atleast one data pattern to be received is centered in relation to theselective part of the transmission bandwidth.

Further advantageously, the receiver can be tuned to receive a selectivepart of said transmission bandwidth on the basis of signallinginformation received in a signalling pattern of a previous frame.

It has to be understood that the present invention can be applied to anykind of multi-carrier system in which a transmitting apparatus isadapted to transmit data in an entire transmission bandwidth and areceiving apparatus is adapted to selectively receive only a part ofsaid entire transmission bandwidth. Non limiting examples for suchsystems may be existing or future uni-directional or bi-directionalbroadcast systems, such as wired or wireless (for example cable based,terrestrial etc.) digital video broadcast systems. The non limitingexample for a multi-carrier system would be an orthogonal frequencydivision multiplex (OFDM) system, however, any other suitable systemcould be used in which data, pilot signals and the like are mapped on aplurality of frequency carriers. The frequency carriers may hereby beequidistant and respectively have the same length (bandwidth). However,the present invention may also be used in multi-carrier systems in whichthe frequency carriers are not equidistant and/or do not have therespectively same length. Further, it should be understood that thepresent invention is not limited to any kind of specific frequency rangeneither in the overall transmission bandwidth applied on thetransmitting side nor on the selected part of the transmission bandwidthto which the receiving side is tuned. However, in some applications itmight be advantageous to use a receiving bandwidth on the receivingside, i.e. a bandwidth for the part of the transmission bandwidth towhich the receiver can be tuned, which corresponds to the bandwidth ofreceiving devices of existing (digital video broadcast or other)systems. A non limiting example for a receiver bandwidth may be 8 MHz,i.e. the receiving side can be tuned to any wanted 8 MHz bandwidth fromthe overall transmission bandwidth. Hereby, the overall transmissionbandwidth could be a multiple of 8 MHz, for example 8 MHz, 16 MHz, 24MHz, 32 MHz etc, so that the segmentation of the overall transmissionbandwidth, i.e. length of each training pattern could be 8 MHz. However,other segmentations are possible, e.g. (but not limited to) a length ofeach training pattern of 6 MHz.

Generally, in case of the non limiting example of 8 MHz for the receiverbandwidth, the length of each of the training patterns used in the framestructure of the present invention would be also 8 MHz (or less).

The present invention is explained in more detail in the followingdescription of preferred embodiments in relation to the encloseddrawings, in which

FIG. 1 shows a schematic diagram of an entire transmission bandwidthfrom which a selected part can be selectively and flexibly received by areceiver,

FIG. 2 shows an example for a segmentation of the overall transmissionbandwidth,

FIG. 3 shows a schematic time domain representation of a frame structureaccording to the present invention,

FIG. 4A shows a frequency domain example of a training pattern,

FIG. 4B shows a time domain representation of the training pattern ofFIG. 4A,

FIG. 5A shows a frequency domain representation of a further example ofa training pattern,

FIG. 5B shows a time domain representation of the training pattern ofFIG. 5A,

FIG. 6 shows a schematic frequency domain representation of an overalltransmission bandwidth with repetitive training patterns according tothe present invention.

FIG. 7 shows a simulation result of an auto-correlation of multi-carriersystem in which the transmission bandwidth is equal to the receptionbandwidth,

FIG. 8 shows a simulation result for an auto-correlation in which thereceiving bandwidth coincides with a training pattern according to thepresent invention,

FIG. 9 shows a simulation result of an auto-correlation in case that thereceiving bandwidth does not coincide with a training pattern accordingto the present invention,

FIG. 10 shows a schematic example of a frame structure or patternaccording to the present invention,

FIG. 11 shows a part of the frame structure of FIG. 10 with anexplanation of a reconstruction of a signalling pattern,

FIG. 12 shows a schematic example of a receiver filter characteristic,

FIG. 13 shows a further example of a frame structure of patternaccording to the present invention,

FIG. 14 shows a part of a further example of a frame structure orpattern according to the present invention,

FIG. 15 schematically shows an example of a frame structure of thepresent invention in the time dimension,

FIG. 16 shows a schematic block diagram of an example of a transmittingapparatus according to the present invention, and

FIG. 17 shows a schematic block diagram of an example of a receivingapparatus according to the present invention

FIG. 1 shows a schematic representation of an entire transmissionbandwidth 1, in which a transmitting apparatus according to the presentinvention, as for example the transmitting apparatus 54 schematicallyshown in FIG. 16, transmits signals in a multi-carrier system in linewith the present invention. FIG. 1 further schematically shows a blockdiagram of a receiving apparatus 3 of the present invention, which isadapted to be tuned to and selectively receive a selected part 2 of thetransmission bandwidth 1. Hereby, the receiving apparatus 3 comprises atuner 4 which is adapted to be tuned to and selectively receive thewanted part 2 of the transmission bandwidth 1 as well as furtherprocessing means 5 which perform the further necessary processing of thereceived signals in line with the respective communication system, suchas a demodulation, channel decoding and the like. A more elaborateexample of a receiving apparatus according to the present invention isshown in the schematic block diagram of FIG. 17, which shows a receivingapparatus 63 comprising a receiving interface 64, which can for examplebe an antenna, an antenna pattern, a wired or cable-based receivinginterface or any other suitable interface adapted to receive signals inthe respective transmission system or communication system. Thereceiving interface 64 of the receiving apparatus 63 is connected to areceiving means 65 which comprises a tuning means, such as the tuningmeans 4 shown in FIG. 1 as well as further necessary processing elementsdepending on the respective transmission or communication system, suchas down conversion means adapted to down convert the received signal toan intermediate frequency or the base band.

As stated above, the present invention enables a flexible and changingreception of a wanted part 2 of the transmission bandwidth 1 in areceiver by providing a specific and new frame structure for amulti-carrier system. FIG. 2 shows a schematic representation of anoverall transmission bandwidth 1, within which a transmitting apparatus54 of the present invention is adapted to transmit data content, such asvideo data, audio data or any other kind of data, in different segmentsor parts 6, 7, 8, 9 and 10. For example, the parts 6, 7, 8, 9 and 10could be used by the transmitting apparatus 54 to transmit differentkinds of data, data from different sources, data intended for differentrecipients and so forth. The parts 6 and 9 have for example a maximumbandwidth, i.e. the maximum bandwidth which can be received by acorresponding receiving apparatus 63. The parts 7, 8 and 10 have smallerbandwidths. The present invention now suggests to apply a framestructure or pattern to the entire transmission bandwidth 1 whereby eachframe comprises at least two training patterns adjacent to each other inthe frequency direction and a number of data patterns. Each trainingpattern of a frame will have the same length and the identical pilotsignals. In other words, the overall transmission bandwidth 1 is dividedinto equal parts for the training patterns, whereby the maximumbandwidth to which a receiver can be tuned, for example the bandwidthshown for parts 6 and 9 in FIG. 2, has to be equal or larger than thelength of each training pattern. Hereby, by properly receiving an entiretraining pattern, a receiving apparatus 63 according to the presentinvention can correctly synchronize to the transmitting apparatus 54 andtune to and receive the wanted data in a flexible and non limiting way.Additionally, a frequency offset calculation and/or a channel estimationis/are possible in the receiving apparatus 63 on the basis of such areceived training pattern. It is further clear that the length of thevarious data parts in the transmission bandwidth cannot exceed thelength (number of frequency carriers) of the training patterns in therespective frame as will be explained in more detail further below.

FIG. 3 shows a schematic representation of a time domain structure offrames 11, 11′, 11″ according to the present invention. Each frame 11,11′, 11″ comprises a preamble symbol (or training symbol) 12, 12′, 12″,one or more signalling symbols 13, 13′ and several data symbols 14, 14″.Hereby, in the time domain, the preamble symbols or training symbols arepreceding the signalling symbols which are preceding the data symbols.Each frame 11, 11′, 11″ may have a plurality of data symbols, whereinsystems are possible in which the number of data symbols in each frame11, 11′, 11″ varies. The preamble symbols are used in a receivingapparatus 63 to perform time synchronisation and eventually additionaltasks, such as channel estimation and/or frequency offset calculation.The signalling symbols 13, 13′, contain signalling information, forexample all physical layer information that is needed by the receivingapparatus 63 to decode the received signals, such as but not limited toL1 signalling data. The signalling data may for example comprise theallocation of data content to the various data patterns, i.e. forexample which services, data streams, modulation, error correctionsettings etc. are located on which frequency carriers, so that thereceiving apparatus 63 can obtain information to which part of theentire transmission bandwidth it shall be tuned. Further, the signallingsymbols may contain signalling data indicating the offset of therespective data pattern from the preamble or training pattern and/or thesignalling pattern so that the receiving apparatus 63 may optimize thetuning to the wanted part of the transmission frequency in a way thatthe receipt of the training patterns and/or the signalling patterns isoptimized. The use of the frame structure according to the presentinvention has the further advantage that by dividing the data streaminto logical blocks, changes of the frame structure can be signalledfrom frame to frame, whereby a preceding frame signals the changed framestructure of the or one of the succeeding frames. For example, the framestructure allows a seamless change of modulation parameters withoutcreating errors.

FIGS. 4A, 4B, 5A and 5B show non limiting examples of preamblestructures which could be used in the present invention. It has to beunderstood, however, that other possible preamble structures could alsobe used. FIG. 4A shows a frequency domain representation of a preambleor training pattern 15 in which a plurality of frequency carriers 16 (inthe shown example 2048 carriers), respectively carry a pilot signal. Inother words, all frequency carriers of the training pattern 15 carry apilot signal. FIG. 4B shows the training pattern of FIG. 4A after thetransformation in the time domain. The time domain training symbolcomprises a plurality of time domain samples 17 (in the shown example2048 samples) in a single repetition. In other words, the time domaintraining symbol does not have any repetitions in the time domainsamples. FIG. 5A shows a further non limiting example of a frequencydomain preamble pattern 18, comprising a plurality of frequency carriers(in the shown example 512 carriers). In the shown example, only everyfourth sub-carrier carries a pilot signal 19, all other sub-carriers 20do not carry pilot signals. After transformation into the time domain,the time domain preamble or the training symbol 21 shown in FIG. 5Bshows four repetitions 22, each repetition 22 having the identicalsamples 23 (same value and number). In the shown example, the timedomain training symbol has a length of 2048 time samples and eachrepetition 22 comprises 512 samples. The general rule is that the numberof repetitions in the time domain corresponds to the repetition rate ofthe pilot signals in the frequency domain. In case that the distance ofthe pilot signals in the frequency domain is higher, the number ofrepetitions in the time domain increases. The repetitions in the timedomain preamble or training symbol are sometimes called ‘shortened’training symbols. In the example of FIG. 5B, the time domain symbol thuscomprises four shortened training symbols. In some applications it maybe advantageous to use pseudo noise pilot signal sequences in order toobtain pseudo noise like signal patterns in the time domain. Also, a socalled CAZAC (constant amplitude zero auto correlation) sequence couldbe used for the pilot signals, or any other suitable sequence resultingin pseudo noise like signal patterns and having good correlationproperties both in the frequency as well as in the time domain. Suchsequences allow a time synchronisation in a receiving apparatus 63 ofthe present invention. In addition hereto, such sequences allow areliable channel estimation in the receiving apparatus 63 in case thatthe Nyquist criterion is fulfilled in the frequency dimension. Further,such sequences allow a frequency offset calculation and/or a channelestimation in the receiving apparatus 63.

As mentioned above, the present invention suggests a frequency domainframe structure or frame pattern for the entire transmission bandwidthof the transmitting apparatus 54, in which identical training patternsare repeated over the entire transmission bandwidth, i.e. immediatelyadjacent to each other in the frequency direction. FIG. 6 visualizesschematically such a sequence of identical and adjacent trainingpatterns 25, 26, 27, 28 in an entire transmission bandwidth 24. In otherwords, the same sequence of pilot signals is mapped onto the frequencycarrier of each training pattern 25, 26, 27, 28, so that each trainingpattern has the same length (or bandwidth) and the same number offrequency carriers (assumed that the frequency sub-carriers areequidistant and respectively have the same length or bandwidth).Advantageously, as shown in FIG. 6, the overall transmission bandwidth24 is equally divided into the training patterns 25, 26, 27, 28 havingrespectively the same length. The length of the training patterns 25,26, 27 and 28 also corresponds to the minimum tuning bandwidth to whichthe receiving apparatus 63 of the present invention can be tuned inorder to receive signals, in order to ensure that the receivingapparatus 63 is always able to receive an entire training pattern forsynchronisation (and channel estimation, and/or frequency offsetcalculation).

The present invention therefore enables a receiving apparatus 63 to betuned to any position within the overall channel bandwidth 24 in a veryflexible manner while still being able to perform a reliablesynchronisation by correlating the received pilot signals for example ina correlation means 67 of the transmitting apparatus 63 as shown in FIG.17. Again, the invention suggests to divide the entire transmissionfrequency bandwidth 24 into adjacent sub-blocks or segments each havinga training pattern containing a repetition of the identical pilot signalsequence and thus having the same length. The length of each of thetraining pattern thus corresponds advantageously to the bandwidth towhich the receiving apparatus 63 can be tuned. For example, as shown inFIG. 17, the receiving apparatus 63 comprises a receiving interface 64,such as an antenna, a wired receiving interface or the like, to whichsignals are received in a receiving means 65, which comprises a tuner.If the receiving apparatus 63 is tuned to a part of the transmissionbandwidth which matches or coincides to one of the training patterns,the pilot signal sequence is received in the original order. If thereceiving apparatus 63 is tuned to an arbitrary part of the transmissionbandwidth or for example between two training patterns, still all pilotsignals of the training pattern are received, however, not in theoriginal sequence. However, due to the cyclic behaviour of the pilotsequence sequences, very good correlation properties are still presentparticularly if pseudo noise sequences are used for the pilot signals ineach training pattern and the correlation means 67 of the receivingapparatus 63 of the present invention still delivers good results whenperforming an auto-correlation i.e. a correlation of the received pilotsignals with themselves. Specifically, in wired systems, such as cablesystems, auto-correlation is expected to deliver good results because ofthe high signal to noise ratio. Also, such sequences enable a frequencyoffset calculation and/or a channel estimation in the receivingapparatus 63.

FIG. 7 shows an example of a simulation result for 64 sample pseudonoise sequence for a multi-carrier system without segmentation of thetraining pattern, i.e. in which the transmission bandwidth is identicalto the receiving bandwidth. The correlation peak is clearly visible.FIG. 8 shows a further example of a simulation result for a systemaccording to the present invention, in which the entire transmissionbandwidth comprises identical training patterns and the receiver istuned to a part of the transmission bandwidth. In the simulation shownin FIG. 8, the receiver was tuned and identically matched to the firstsegment, i.e. the first training pattern of the entire transmissionbandwidth. In other words, the simulation shows an auto-correlationresult for the situation in which the receiver receives the pilotsignals of a training pattern in the original sequence. Again, thecorrelation peak is clearly visible. FIG. 9 now shows a simulationresult for the system of FIG. 8, whereby the receiver was tuned to aposition between two training patterns so that the receiver did notreceive the pilot signals in the original sequence, but received thelast part of a preceding training pattern before the first part of thesucceeding training pattern. However, due to the cyclic behaviour of thepilot sequences and the training patterns, it is still possible toobtain an auto-correlation peak, which is shown in FIG. 9.

In case that the receiving apparatus 63 knows its tuning position, i.e.knows the offset from the start of a frame or from the respective startof each training pattern, an optionally provided rearranging means 66could rearrange the received pilot signals into the original sequenceand to perform a cross-correlation on the basis of a comparison with astored version of the expected training pattern in order to obtain across-correlation result. Such a cross-correlation result will normallyhave a better quality then an auto-correlation result since it is lesseffected by noise. Thus, for systems with low signal to noise ratios,cross correlation would be the better choice.

FIG. 10 shows a schematic example of a frequency domain representationof a frame structure or pattern 29 according to the present invention.The frame structure 29 covers the entire transmission bandwidth 24 inthe frequency direction and comprises at least two training patterns 30adjacent to each other in the frequency direction, each carrying theidentical sequence of pilot signals on respective frequency carriers andhaving the same length. In the example shown in FIG. 4, the entiretransmission bandwidth 24 is sub-divided into four training patterns 30,but any other higher or lower number of training patterns might besuitable. In the transmitting apparatus 54 of the present invention asshown in FIG. 16, a pilot mapping means 55 is adapted to map the pilotsignals onto the frequency carriers of each training pattern.Advantageously, a pseudo noise sequence or a CAZAC sequence is used forthe pilot signals, but any other sequence with good pseudo noise and/orcorrelation properties might be suitable. Also, the pilot mapping means55 may be adapted to map a pilot signal onto every frequency carrier inthe training patterns, as explained in relation to FIG. 4.Alternatively, the pilot mapping means 55 might be adapted to map apilot signal onto every m-th frequency carrier (m being a natural numberlarger than 1) as for example explained in relation to FIG. 5. Thelength or bandwidth 39 of every training pattern 30 is the same as thebandwidth 38 to which the tuner of the receiving apparatus 63 can betuned. However, the part of the transmission bandwidth to which thetuner of the receiving apparatus 63 can be tuned, may be larger than thelength of a training pattern 30. Besides for the correlation performedin the correlation means 67 in the receiving apparatus 63, the receivedpilots can further (after transformation into the frequency domain inthe transformation means 68) be used for a channel estimation for thefrequency carriers in the frame in a channel estimation means 69, whichprovides a de-mapping means 70 with the necessary channel estimationinformation enabling a correct de-mapping of the data in the receiveddata signals. Also, the received pilots can be used in the receivingapparatus 63 for a frequency offset calculation in a corresponding meanswhich is not shown in FIG. 17.

The frame structure or pattern 29 further comprises at least twosignalling patterns 31 adjacent to each other in the frequency directionwhich follow the training patterns 30 in the time direction. Eachsignalling pattern 31 has the same length and bandwidth as therespectively preceding training pattern 30, and the beginning and theend of each signalling pattern 31 in the frequency direction areidentical to the beginning and the end of the respective (time wise)preceding training pattern 30, so that the frequency structure of thesignalling patterns 31 is identical to the frequency structure of thetraining patterns 30. In other words, the signalling patterns 31 arealigned to the training patterns 30. The transmitting apparatus 54 ofthe present invention shown in FIG. 16 comprises a signalling datamapping means 57 which is adapted to map signalling data onto thefrequency carriers of each signalling pattern 31. Hereby, eachsignalling pattern 31 comprises for example the location of thesignalling pattern 31 within the frame. For example each signallingpattern 31 in each frame has and carries the identical signalling data,except the location of the respective signalling pattern in the frame,which is different in each signalling pattern 31 in a frame. Thesignalling data are for example L1 signalling data which contain allphysical layer information that is needed by the receiving apparatus 63to decode received signals. However, any other suitable signalling datamay be comprised in the signalling patterns 31. The signalling patterns31 might for example comprise the location of the respective datasegments 32, 33, 34, 35, 36 so that a receiving apparatus 63 knows wherethe wanted data segments are located so that the tuner of the receivingapparatus 63 can tune to the respective location in order to receive thewanted data segments. As shown in FIG. 17, the receiving apparatus 63,after the receiving means 65 with the tuner, comprises a transformationmeans 68 for transforming the received time domain signals into thefrequency domain, where after the signalling data (after an optionalreconstruction in a reconstruction means 71), are de-mapped in ade-mapping means 72 and then evaluated in an evaluation means 73. Theevaluation means 73 is adapted to extract the necessary and requiredsignalling information from the received signalling data. If necessary,additional signalling patterns could be provided in the time directionimmediately succeeding the signalling patterns 31.

The frame structure or pattern 29 further comprises at least two datasegments extending over the entire frequency bandwidth 24 in thefrequency direction and following the signalling patterns 31 in the timedirection. In the time slot immediately following the time slot in whichthe signalling patterns 31 are located, the frame structure 29 showsseveral data segments 32, 33, 34, 35, 36 and 37 with different lengths,i.e. a different number of respective frequency carriers onto which dataare mapped. The frame structure 29 further comprises additional datasegments in succeeding time slots, whereby the additional data patternsrespectively have the same length and number of frequency carriers asthe respectively preceding data pattern. For example, the data pattern32′, 32″ and 32′″ have the same length as the first data pattern 32. Thedata patterns 33′, 33″ and 33′″ have the same length as the data segment33. In other words, the additional data patterns have the same frequencydimension structure as the several data patterns 32, 33, 34, 35, 36 and37 in the first time slot after the signalling patterns 31. Thus, if thereceiving apparatus 63 for example tunes to a part 38 of thetransmission bandwidth in order to receive the data pattern 35, all timewise succeeding data patterns 35′, 35″ and 35′″ which have the samelength as the data pattern 35 can be properly received.

The flexible and variable data pattern structure of the frame structureor pattern 29 as suggested by the present invention can for example beimplemented in the transmitting apparatus 54 of the present invention asshown in FIG. 16 by mapping of various different data streams, forexample with different kinds of data and/or data from different sources,as visualized by the branches data 1, data 2 and data 3 in FIG. 16. Therespective data are then mapped onto frequency carriers in respectivedata patterns by the respective data mapping means 58, 58′ and 58″. Asstated, at least some of the various data patterns may have differentlengths, i.e. different numbers of frequency carriers in case that thefrequency carriers are equidistant and have the same bandwidth,respectively. Alternatively, the number of data patterns in thefrequency direction may be the same as the number of training patterns,wherein the length (or bandwidth) of each data patterns may be identicalto the length of each training patterns and they may be aligned to eachother (have the same frequency direction structure). Alternatively, eachdata pattern might have the same length and the number of the datapatterns might be a multiple of the number of training patterns, whilestill having the same frequency structure and alignment. Thus forexample, 2, 3, 4 or more data patterns would be aligned to each of thetraining patterns. Generally, the length of the data patterns needs tobe smaller or at maximum equal to the effective receiver bandwidth sothat the data patterns can be received in the receiving apparatus 63.Further, the transmitting apparatus 54 may be adapted to change the datapattern structure, e.g. the length and/or the number of the datapatterns dynamically. Alternatively, the structure of the data patternscould be fixed or permanent.

Further, it is to be noted that the data patterns could advantageouslycomprise pilot signals mapped on some of the frequency carriers in orderto enable a fine channel estimation on the receiving side. Hereby, thepilot signal could be scattered among the carriers with the data in aregular or an irregular pattern depending.

In the transmitting apparatus 54, the frequency carriers with the pilotsfrom the pilot mapping means 55, the frequency carriers with thesignalling data from the signalling mapping means 57 and the frequencycarriers with the data from the various data mapping means 58, 58′, 58″are then combined to a frame pattern or structure 29 according to thepresent invention in a frame forming means 59.

Generally, the frame structure of the present invention could be fixedor permanent, i.e. the overall bandwidth as well as the extension ofeach frame in the time direction could be fixed and always the same.Alternatively, the frame structure can also be flexible, i.e. theoverall bandwidth and/or the extension of each frame in the timedirection could be flexible and changed from time to time depending onthe desired application. For example, the number of time slots with datapatterns could be flexibly changed. Hereby, the changes could besignalled to a receiving apparatus in the signalling data of thesignalling patterns.

It can be seen in FIG. 10, that the part 38 to which the receivingapparatus 63 is tuned, does not match with the frequency structure ofthe training patterns 30 and signalling patterns 31. However, isexplained above, due to the cyclic nature of the pilot signal sequencesin the training patterns 30, the correlation means 67 of the receivingapparatus 63 is still able to perform an auto-(or cross-)correlation.Further, in this situation shown in FIG. 10, the receiving apparatus 63needs knowledge about the offset of the part 38 in relation to thefrequency structure of the frame pattern 29 in order to be able tore-arrange the receive signalling carriers into the original signallingsequence of the signalling patterns 31 which is done in a reconstructionmeans 71. This is due to the fact that the signalling patterns 31 havethe same length and frequency structure as the training patterns 30.

During the start-up phase or initialization phase of the receivingapparatus 63, the receiving apparatus 63 may tune to an arbitraryfrequency part of the overall transmission bandwidth. In thenon-limiting example of a cable broadcast system, the training pattern30 could for example have a 8 MHz bandwidth. Thus, during the start-upphase, the receiving apparatus 63 is able to receive an entire trainingpattern 30 in the original or re-ordered sequence as well as an entiresignalling pattern 31 in the original or re-ordered sequence from thereceived training pattern 30. The receiving apparatus 63 is able toperform a correlation in the correlation means 67 in order to obtain atime synchronisation, as well as perform a channel estimation (usually acoarse channel estimation) in a channel estimation means 69 and/or afrequency offset calculation after a transformation of the received timedomain signals into the frequency domain in the transformation means 68.In the evaluation means 73 of the receiving apparatus 63, the receivedsignalling data are evaluated, for example the location of the receivedsignalling pattern in the frame is obtained so that the receiver canfreely and flexibly tune to the respectively wanted frequency position,such as the part 38 is shown in FIG. 10. In the new tuning position,which will usually not necessarily match with the frequency structure ofthe training patterns 30 and the signalling patterns 31, the receivingapparatus 63 is still able to perform synchronisation, channelestimation and frequency offset calculation on the basis of the pilotsignals of the training patterns 30 due to their cyclic nature. However,in order to be able to properly evaluate the signalling data of thesignalling patterns 31, the received signalling signals have to bere-ordered which is performed in a reconstructing means 71 as described.FIG. 11 shows this reordering in a schematic example. The last part 31′of a previous signalling pattern is received before the first part 31″of a succeeding signalling pattern, where after the reconstructionsmeans 71 places the part 31′ after the part 31″ in order to reconstructthe original sequence of the signalling data, where after the reorderedsignalling pattern is evaluated in the evaluation means 73 after acorresponding de-mapping of the signalling data from the frequencycarriers in the de-mapping means 72. It is to be remembered that thecontent of each signalling pattern 31 is the same, so that thisreordering is possible.

Often, a receiving apparatus does not provide a flat frequency responseover the complete receiving bandwidth to which the receiver is tuned. Inaddition, a transmission system usually faces increasing attenuation atthe boarder of the receiving bandwidth window. FIG. 12 shows a schematicrepresentation of a typical filter shape example. It can be seen thatthe filter is not rectangular, so that e.g. instead of 8 MHz bandwidth,the receiving apparatus is only able to effectively receive 7.4 MHzbandwidth. The consequence is that the receiving apparatus 63 may not beable to perform the reordering of the signalling data as described inrelation to FIG. 11 in case that the signalling patterns 31 have thesame length and bandwidth as the receiving bandwidth of the receivingapparatus 63, so that some signals are lost and cannot be received atthe border of the receiving bandwidth. In order to overcome thisproblem, and other problems and in order to ensure that the receivingapparatus 63 is always able to receive one complete signalling patternsin the original sequence and does not have to reorder or rearrange thereceived signalling signals, the present invention alternatively oradditionally suggests to use signalling patterns 31 a which have areduced length as compared to the training patterns 30. The exampleshown in FIG. 13, it is suggested to use signalling patterns 31 a whichhave exactly half the length of a training pattern 30, but still thesame frequency structure as the training patterns 30. In other words,respective two (i.e. pairs) of the half length signalling patterns 31 aare matched and aligned with each one of the training patterns 30 asshown in FIG. 13. Hereby, each pair of signalling patterns 31 a wouldhave the identical signalling data including the location of thesignalling patterns 31 a in the respective frame. However, in relationto the other pairs of signalling patterns, in these other pairs, sincethey have a respective different location within the frame, thesignalling data would be identical except the location information.Hereby, in order to ensure that the same amount of signalling data asbefore can be transmitted, it might be necessary to add additional halflength signalling patterns 31 b in the time slot succeeding thesignalling patterns 31 a and before the data patterns 32, 34, 35, 36 and37. The additional signalling patterns 31 b have the same time andfrequency arrangement/alignment as the signalling patterns 31 a, butcomprise additional and different signalling information as thesignalling information contained in the signalling patterns 31 a. Inthis way, the receiving apparatus 63 will be able to receive thesignalling patterns 31 a and 31 b completely and in the originalsequence so that a reconstruction or reordering is not necessary. Inthis case, the reconstruction means 71 in the receiving apparatus 63 canbe omitted. It is also possible to only provide one time slot with halflength signalling patterns 31 a if all necessary signalling data can betransmitted in the half length and the additional signalling patterns 31b are not necessary. Alternatively, even more half length signallingpatterns could be used in the succeeding time slot after the signallingpatterns 31 b.

It should be generally (for all embodiments of the present invention)noted that the length (or bandwidth) of the training patterns, the datapatterns and/or the signalling patterns could be adapted to, e.g. couldbe smaller than or at maximum equal to, the effective receivingbandwidth of the receiving apparatus 63, for example the outputbandwidth of the receiving band pass filter, as described above.

Further, it should be generally noted that the training patterns, thesignalling patterns and/or the data patterns of the frame structuredescribed by the present invention could comprise additional guardbands, i.e. unused carriers at the beginning and/or the end of therespective pattern or frame. For example, each training pattern couldcomprise a guard band at the beginning and the end of each pattern.Alternatively, in some applications it might be advantageous if only thefirst training pattern in each frame, in the example of FIG. 10 thetraining pattern at position 39, could comprise a guard band only at thebeginning of the pattern, and the last training pattern in each framecould comprise a guard band only at the end of the pattern.Alternatively, in some applications only the first training pattern ineach frame, in the example of FIG. 10 the training pattern at position39, could comprise a guard band at the beginning as well as at the endof the pattern, and the last training pattern in each frame couldcomprise a guard band at the beginning as well as at end of the pattern.The length of the guard band comprised in some or all of the trainingpatterns could for example be smaller or at maximum equal to the maximumfrequency offset the receiving apparatus can cope with. In the mentionedexample of a bandwidth of 8 MHz for each training pattern, the guardband could for example have a length of 250 to 500 kHz or any othersuitable length. Also, the length of each of the guard bands comprisedin the training patterns could be at least the length of the carrierswhich are not received in the receiving apparatus due to the filtercharacteristics as described in relation to FIG. 12. Also, in case thatthe signalling patterns have guard bands, the length of each of theguard bands comprised in the training patterns could be at least thelength of each of the signalling pattern guard bands.

Additionally or alternatively, each signalling pattern could comprise aguard band with unused carriers at the beginning and the end of eachpattern. Hereby, the length of each of the guard bands comprised in thesignalling patterns could be at least the length of the carriers whichare not received in the receiving apparatus due to the filtercharacteristics as described in relation to FIG. 12, so that the lengthof the signalling data in each signalling pattern is equal to (or may besmaller than) the effective receiver bandwidth.

Additionally or alternatively, each data pattern could comprise a guardband with unused carriers at the beginning and the end of each pattern.Hereby, the length of the guard bands could for example be the same asthe length of the guard bands of the signalling patterns if thesignalling patterns comprise guard bands. Alternatively, in someapplications only the respective first data patterns in each frame inthe frequency direction, in the example of FIGS. 10 and 13 the datapatterns 32, 32′, 32″, 32′″ could comprise a guard band only at thebeginning of the data pattern, and the last data patterns in each framein the frequency direction, in the example of FIGS. 10 and 13 the datapatterns 37, 37′, 37″, 37′″ could comprise a guard band at the end ofthe data pattern. Hereby, the length of the guard bands of the datacarriers could be the same as (or could be different from) the length ofthe guard bands of the signalling patterns.

Alternatively or additionally, in order to overcome the problem thatparts of the signalling patterns 31 may not be receivable in thereceiving apparatus 63, the transmitting apparatus 54 could optionallycomprise an error coding means 56 adapted to add some kind of errorcoding, redundancy, such as repetition coding, or the like to thesignalling data which are mapped onto the frequency carriers of asignalling pattern by the signalling mapping means 57. The additionalerror coding would enable the transmitting apparatus 54 to usesignalling patterns 31 in the same length as the training patterns 30,as shown in FIG. 10, since the receiving apparatus 63 is able, forexample, by means of the reconstructing means 71, to perform some kindof error detection and/or correction in order to reconstruct theoriginal signalling pattern.

In order to ensure a even better reception of the signalling patternsand the receiving apparatus 63, the present invention further suggeststo optimize the tuning position of the receiving apparatus 63. In theexamples shown in FIGS. 10 and 13, the receiver is tuned to a part 38 ofthe transmission bandwidth by centering the part 38 around the frequencybandwidth of the data patterns to be received. Alternatively, thereceiving apparatus 63 could be tuned so that the reception of thesignalling pattern 31 is optimized by placing the part 38 so that amaximum part of a signalling pattern 31 is received while the wanteddata pattern is still fully received. Alternatively, the presentinvention suggests that the length of the respective data patternsshould not be different from the length of the respective preamblepatterns 30 and signalling patterns 31 by more than a certain percentagefor example 10%. An example for this solution can be found in FIG. 14.The borders between the data patterns 42, 43, 44 and 45 are (in thefrequency direction) not deviating from the borders between preamblepatterns 30 and the signalling patterns 31 by more than a certainpercentage, such as (but not limited to) 10%. This small percentage canthen be corrected by the above-mentioned additional error coding in thesignalling patterns 31.

FIG. 15 shows a time domain representation of an example of frame 47according to the present invention. In the transmitting apparatus 54,after the frame pattern or structure was generated in the frame formingmeans 59, the frequency domain frame pattern is transformed into thetime domain by a transformation means 60. An example of a resulting timedomain frame is now shown in FIG. 15. The frame 47 comprises a number ofshortened training symbols 48, resulting from a mapping of pilot signalsonly onto every m-th frequency carrier (m being a natural number largeror equal than 2) by a pilot mapping means 55, followed by a guardinterval 49, a signalling symbol 50, a further guard interval 51 and anumber of data symbols 52, which are respectively separated by guardintervals 53. In case of the presence of respective two signallingpatterns 31 a, 31 b as explained in relation to FIG. 13, the frame 47would comprise two signalling symbols separated by a guard interval. Theguard intervals could e.g. be cyclic extensions of the useful parts ofthe respective symbols. The synchronization reliability could begenerally enhanced by inverting the last training symbol, i.e. byinverting the phase of the last training symbol in respect to thepreceding training symbols (which have all the same phase). The timedomain frames are then forwarded to a transmission means 61 whichprocesses the time domain signal depending on the used multi-carriersystem, for example by up-converting the signal to the wantedtransmission frequency. The transmission signals are then transmittedvia a transmission interface 62, which can be a wired interface or awireless interface, such as an antenna or the like.

The number of shortened training symbols 48 in frame 47 is depending onthe wanted implementation and the used transmission system. As anon-limiting example, the number of shortened training symbols 48 couldbe 8, which is a good compromise between correlation complexity andsynchronization reliability.

FIG. 15 further shows that a respective number of frames could becombined to super frames. The number of frames per super frame, i.e. thelength of each super frame in the time direction, could be fixed orcould vary. Hereby, there might be a maximum length up to which thesuper frames could be set dynamically. Further, it might be advantageousif the signalling data in the signalling patterns for each frame in asuper frame are the same and if changes in the signalling data onlyoccur from super frame to super frame. In other words, the modulation,coding, number of data patterns etc. would be the same in each frame ofa super frame, but could then be different in the succeeding superframe. For example, the length of the super frames in broadcast systemscould be longer since the signalling data might not change as often, andin interactive system the super frame length could be shorter since anoptimization of the transmission and reception parameters could be doneon the basis of feedback from the receiver to the transmitter.

The elements and functionalities of the transmitting apparatus 54, ablock diagram of which is shown in FIG. 16, have been explained before.It has to be understood, that an actual implementation of a transmittingapparatus 54 will contain additional elements and functionalitiesnecessary for the actual operation of the transmitting apparatus in therespective system. In FIG. 16, only the elements and means necessary forthe explanation and understanding of the present invention are shown.The same is true for the receiving apparatus 63, a block diagram ofwhich is shown in FIG. 17. FIG. 17 only shows elements andfunctionalities necessary for the understanding of the presentinvention. Additional elements will be necessary for an actual operationof the receiving apparatus 63. It has to be further understood that theelements and functionalities of the transmitting apparatus 54 as well asthe receiving apparatus 63 can be implemented in any kind of device,apparatus, system and so forth adapted to perform the functionalitiesdescribed and claimed by the present invention.

The present invention is further directed to a frame structure (and acorrespondingly adapted transmitting and receiving apparatus and methodas described above), which, as an alternative to the above describedembodiments, does have a number (two or more) data patterns in which atleast one data pattern has a length which is different from the lengthof the other data pattern(s). This structure of data patterns with avariable length can be combined either with a sequence of trainingpatterns with identical lengths and contents as described above, or witha sequence of training patterns in which at least one training patternhas a length and/or a content different from the other trainingpatterns, i.e. a variable training pattern length. In both cases, thereceiving apparatus 63 will need some information about the varying datapattern length, which could be transmitted by means of a separatesignalling data channel or by means of signalling data comprised insignalling data patterns comprised in the frame structure as describedabove. In the later case, it might be a possible implementation if thefirst training pattern and the first signalling pattern in each framealways have the same length so that the receiving apparatus can alwaysobtain the information about the varying data patterns by receiving thefirst training patterns and signalling patterns in every or thenecessary frames. Of course, other implementations might be possible.Otherwise, the rest of the above description in relation to the trainingpatterns, the data patterns and the signalling patterns as well as thepossible implementations in the transmitting apparatus 54 and thereceiving apparatus 63 is still applicable.

The invention claimed is:
 1. A transmitting apparatus for transmittingsignals in a multi-carrier system on the basis of a frame structure,said transmitting apparatus comprising: a frame former configured toform frames of said frame structure, each frame comprising at least twopreamble patterns adjacent to each other in the frequency direction andat least two data patterns following the at least two preamble patternsin the time direction, wherein all data patterns following each other inthe time direction have a same frequency direction structure, each ofthe at least two preamble patterns and the at least two data patternscomprising a plurality of frequency carriers, wherein a length of eachof the at least two preamble patterns is equal to or smaller than theeffective receiving bandwidth of a receiving apparatus configured toreceive said signals, a pilot mapper configured to map pilot signals onfrequency carriers of each of said at least two preamble patterns in aframe, each preamble pattern having a same length, a data mapperconfigured to map data on frequency carriers of said at least two datapatterns in a frame, a transformer configured to transform said at leasttwo preamble patterns and said at least two data patterns from thefrequency domain into the time domain in order to generate a time domaintransmission signal, and a transmitter configured to transmit said timedomain transmission signal.
 2. The transmitting apparatus according toclaim 1, wherein a length of at least some of the at least two datapatterns is different from each other, and the length of each of the atleast two data patterns is smaller than or equal to the length of eachof the at least two preamble patterns.
 3. The transmitting apparatusaccording to claim 1, wherein a length of all the at least two datapatterns is smaller than or equal to the length of each of the at leasttwo preamble patterns.
 4. The transmitting apparatus according to claim1, wherein the length of the at least two data patterns is adjusteddynamically.
 5. The transmitting apparatus according to claim 1, whereineach frame comprises at least two signaling patterns, said transmittingapparatus further comprising a signaling data mapper configured to mapthe same signaling data on frequency carriers of each signaling patternin a frame.
 6. The transmitting apparatus according to claim 5, whereina length of each signaling pattern is the same as the length of said atleast two preamble patterns.
 7. The transmitting apparatus according toclaim 5, wherein a length of each signaling pattern is smaller than thelength of each of said at least two preamble patterns.
 8. Thetransmitting apparatus according to claim 7, wherein the length of eachsignaling pattern is half the length of each of said at least twopreamble patterns.
 9. The transmitting apparatus according to claim 5,wherein the signaling data mapper is configured to map the signalingdata on frequency carriers of each signaling pattern of the at least twosignaling patterns with an error correction coding.
 10. A transmittingmethod for transmitting signals in a multi-carrier system on the basisof a frame structure, the method comprising: forming frames of saidframe structure, each frame comprising at least two preamble patternsadjacent to each other in the frequency direction and at least two datapatterns following the at least two preamble patterns, wherein all datapatterns following each other in the time direction have a samefrequency direction structure, each of the at least two preamblepatterns and the at least two data patterns comprising a plurality offrequency carriers, wherein a length of each of the at least twopreamble patterns is equal to or smaller than the effective receivingbandwidth of a receiving apparatus configured to receive said signals,mapping pilot signals on frequency carriers of each of said at least twopreamble patterns in a frame, each preamble pattern having a samelength, mapping data on frequency carriers of said at least two datapatterns in a frame, transforming said at least two preamble patternsand said at least two data patterns from the frequency domain into thetime domain in order to generate a time domain transmission signal, andtransmitting said time domain transmission signal.
 11. A receivingapparatus for receiving signals in a multi-carrier system on the basisof a frame structure in a transmission bandwidth, each frame comprisingat least two preamble patterns adjacent to each other in the frequencydirection, each with pilot signals mapped on frequency carriers and atleast two data patterns following the at least two preamble patterns inthe time direction, wherein all data patterns following each other inthe time direction have a same frequency direction structure, said atleast two data patterns having data mapped on frequency carriers, eachof said at least two preamble patterns having a same length, each of theat least two preamble patterns and the at least two data patternscomprising a plurality of frequency carriers, said receiving apparatuscomprising: a receiver configured to be tuned to and to receive aselected part of said transmission bandwidth, said selected part of saidtransmission bandwidth having at least a length of one of said at leasttwo preamble patterns and covering at least one data pattern to bereceived, and a correlator configured to perform a correlation on thebasis of the pilot signals received in said selected part of saidtransmission bandwidth.
 12. The receiving apparatus according to claim11, wherein said correlator is configured to perform an auto-correlationon the basis of the pilot signals received in said selected part of saidtransmission bandwidth.
 13. The receiving apparatus according to claim11, wherein said correlator is configured to perform a cross-correlationon the basis of a comparison between a stored version of a preamblepattern and a received version of a preamble pattern received in saidselected part of said transmission bandwidth.
 14. The receivingapparatus according to claim 13, further comprising a pilot rearrangerconfigured to rearrange said received pilot signals into an originalsequence in case that the selected part of said transmission bandwidthto which the receiver is tuned does not match with a preamble patternstructure.
 15. The receiving apparatus according to claim 11, whereineach frame comprises at least two signaling patterns, each signalingpattern comprising a same signaling data mapped onto frequency carriers,said receiving apparatus further comprising a reconstructor configuredto reconstruct an original signaling pattern from said received selectedpart of said transmission bandwidth.
 16. The receiving apparatusaccording to claim 15, wherein said reconstructor is configured torearrange received signaling signals into the original signaling patternin case that the selected part of said transmission bandwidth to whichthe receiving means is tuned does not match with a signaling patternstructure.
 17. The receiving apparatus according to claim 15, whereinsaid reconstructor is configured to perform an error correction decodingon said received signaling signals in order to reconstruct the originalsignaling pattern.
 18. The receiving apparatus according to claim 15,wherein said receiver is configured to be tuned to and to receive theselected part of said transmission bandwidth so that an optimizedreceipt of a signaling pattern in the selected part of said transmissionbandwidth to be received is enabled.
 19. The receiving apparatusaccording to claim 11, wherein said receiver is configured to be tunedto and to receive the selected part of said transmission bandwidth sothat said at least one data pattern to be received is centered inrelation to the selected part of said transmission bandwidth to bereceived.
 20. The receiving apparatus according to claim 11, whereinsaid receiver is configured to be tuned to and to receive the selectedpart of said transmission bandwidth on the basis of signalinginformation received in a signaling pattern of a previous frame.
 21. Areceiving method for receiving signals transmitted in a multi-carriersystem on the basis of a frame structure in a transmission bandwidth,each frame comprising at least two preamble patterns adjacent to eachother in the frequency direction, each with pilot signals mapped onfrequency carriers and at least two data patterns following the at leasttwo preamble patterns, wherein all data patterns following each other inthe time direction have the same frequency direction structure, said atleast two data patterns having data mapped on frequency carriers, eachof said at least two preamble patterns having a same length, each of theat least two preamble patterns and the at least two data patternscomprising a plurality of frequency carriers, the method comprising:receiving a selected part of said transmission bandwidth, said selectedpart of said transmission bandwidth having at least a length of one ofsaid at least two preamble patterns and covering at least one datapattern to be received, and performing a correlation on the basis of thepilot signals received in said selected part of said transmissionbandwidth.
 22. A system for transmitting and receiving signals,comprising a transmitting apparatus according to claim 1, and areceiving apparatus comprising: a receiver configured to be tuned to andto receive a selected part of said transmission bandwidth, said selectedpart of said transmission bandwidth having at least a length of one ofsaid at least two preamble patterns and covering at least one datapattern to be received, and a correlator configured to perform acorrelation on the basis of the pilot signals received in said selectedpart of said transmission bandwidth.
 23. A method for transmitting andreceiving signals, comprising a transmitting method for transmittingsignals in a multi-carrier system on the basis of a frame structure,said transmitting method comprising: forming frames of said framestructure, each frame comprising at least two preamble patterns adjacentto each other in the frequency direction and at least two data patternsfollowing the at least two preamble patterns, wherein all data patternsfollowing each other in the time direction have a same frequencydirection structure, each of the at least two preamble patterns and theat least two data patterns comprising a plurality of frequency carriers,wherein a length of each of the at least two preamble patterns is equalto or smaller than the effective receiving bandwidth of a receivingapparatus configured to receive said signals, mapping pilot signals onfrequency carriers of each of said at least two preamble patterns in aframe, each preamble pattern having a same length, mapping data onfrequency carriers of said at least two data patterns in a frame,transforming said at least two preamble patterns and said at least twodata patterns from the frequency domain into the time domain in order togenerate a time domain transmission signal, and transmitting saidtransmission signal, said method further comprising the receiving methodaccording to claim 21.